Add workingDirectory in showcase

Author: Rubilmax

.github/workflows/foundry-storage-check.yml

@@ -30,4 +30,5 @@ jobs:
       - name: Check storage layout
         uses: Rubilmax/foundry-storage-check@feat/showcase
         with:
-          contract: contracts/Example.sol:Example
+          contract: Example.sol:Example
+          workingDirectory: contracts/ # optional, could be replaced with `contracts/Example.sol:Example` in the line above